W8.1, Potassium (K) nutrition Flashcards Preview

III - S&PN (Soil & Plant Nutrition) > W8.1, Potassium (K) nutrition > Flashcards

Flashcards in W8.1, Potassium (K) nutrition Deck (16)
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1
Q

True or false?

We apply enough K in australian agriculture.

A

False. For much of the cropland in Australia, we’re in a negative K balance (removal exeeds input); i.e. we’re mining soil K.

Our soils currently have large quantities of K, so there hasn’t been much economic loss from not adding K (yet).

2
Q

Where would you expect K to be concentrated on a farm?

A

Around stock water and rest areas.

Where crop stubble/biomass has been concentrated (e.g. in the same rows).

3
Q

True or false?

Potassium uptake can contribute to rhizosphere acidification.

A

True. Potassium is taken up as K+, and to maintain charge balance, H+ can be exuded.

4
Q

What is the role of potassium in plants?

A
  • Osmoregulation
    • Maintaining turgor
    • Supporting expansive growth (e.g. stem elongation, fruit growth)
    • helps with tolerance to drought, frost, etc.
  • Major cation for maintaining charge balance
  • Activates enzymes (i.e. they can only function properly in the presence of K)
    • e.g. starch synthase
      • = ↑ starch production in crops like potato, sweet potato, tomatoes, grapevines, and sugarcane.
  • Regulates photosynthate translocation
    • higher [K] = higher rate of sap flow in phloem from leaves to fruits
  • Defence against oxidative stress (free radicals)
  • Tolerance to stress
    • biotic and abiotic (net blotch, powdery mildew, frost, drought)
5
Q

True or false?

More potassium = better stress tolerance.

A

True, but only to a point. Adding more K beyond that which would correct a deficiency is unlikely to have any beneficial effect.

6
Q

True or false?

Potassium uptake is related to plant metabolism.

A

True.

Potassium uptake is via specialised K+ channels and relies on a proton pump to maintain charge balance, which is regulated by metabolic activity (so plants that are under stress, photosynthesising slowly, growing slowly, etc. will take up less K than those growing prolifically).

7
Q

Where is most of the K located in a cereal crop, and what are the consequences of this (especially in terms of management)?

A

In the straw.

Means that if you crop in the same row year after year you will get banding of K as the straw breaks down.

Also means that if you export the straw you’re removing a lot of K.

8
Q

True or false?

Potassium availability limits the effectiveness of other nutrients.

A

True (think Liebig’s law of the minimum).

9
Q

True or false?

Potassium deficiency is more common in finely textured soils (clays).

A

False; it’s more common in coarsely-textured soils (it’s adsorbed more readily in clays).

10
Q

True or false?

Potassium and calcium interact negatively (high Ca2+ reduces uptake of K+)

A

False. Potassium and sodium interact strongly, and a high [Na+] will result in reduced K+ uptake. Calcium mediates the antagonism.

11
Q

What kinds of crops need to be supplied with lots of K?

A

Horticultural crops.

12
Q

True or false?

Potassium deficiency is more common in high rainfall areas.

A

True.

13
Q

What other cationic nutrients are antagonistic with potassium?

A

Sodium.

  • Increasing the ability of a plant to exclude sodium will increase it’s uptake of potassium (and vice versa; i.e. the lower the [leaf K], the higher the [leaf Na]).

Magnesium

  • Potassium reduces the uptake of magnesium.
  • The cause of grass tetany (hypomagnaesia (magnesium deficiency)) in ruminants.
14
Q

What are the two potential negative effects of increasing K concentration in citrus?

A

Increased rind thickness and less colour.

Everything else (size, weight, rind creasing, pugging, and splitting, post-harvest storage, and juice quality) are all improved.

15
Q

How does potassium influence grain filling?

A

Starch synthesis in grain depends on potassium (starch synthase), so inadequate K means inadequate grain filling = small grains = higher screenings.

16
Q

What are the (rough) proportions of K in the solution, fixed, and structural pools?

A

< 2% in solution

1-10% fixed (adsorbed)

90-98% structural